Since /sys is unavailable in build environments, the list of available
TCP network interfaces cannot be obtained via /sys/class/net.  This patch
provides alternative code that uses the SIOCGIFCONF ioctl to get the
names of the available TCP network interfaces.

diff --git a/src/uct/tcp/tcp_iface.c b/src/uct/tcp/tcp_iface.c
index 81ad459..10024a6 100644
--- a/src/uct/tcp/tcp_iface.c
+++ b/src/uct/tcp/tcp_iface.c
@@ -12,6 +12,8 @@
 #include <sys/poll.h>
 #include <netinet/tcp.h>
 #include <dirent.h>
+#include <net/if.h>
+#include <sys/ioctl.h>
 
 static ucs_config_field_t uct_tcp_iface_config_table[] = {
   {"", "MAX_SHORT=8k", NULL,
@@ -483,6 +485,70 @@ static UCS_CLASS_DEFINE_NEW_FUNC(uct_tcp_iface_t, uct_iface_t, uct_md_h,
                                  uct_worker_h, const uct_iface_params_t*,
                                  const uct_iface_config_t*);
 
+/* Fetch information about available network devices through an ioctl.  */
+static ucs_status_t query_devices_ioctl(uct_md_h md,
+					uct_tl_resource_desc_t **resource_p,
+					unsigned *num_resources_p)
+{
+    int sock, err, i;
+    uct_tl_resource_desc_t *resources, *tmp;
+    unsigned num_resources;
+    ucs_status_t status;
+    struct ifconf conf;
+    struct ifreq reqs[10];
+
+    conf.ifc_len = sizeof reqs;
+    conf.ifc_req = reqs;
+
+    sock = socket(SOCK_STREAM, AF_INET, 0);
+    if (sock < 0) {
+	ucs_error("socket(2) failed: %m");
+	status = UCS_ERR_IO_ERROR;
+	goto out;
+    }
+
+    err = ioctl(sock, SIOCGIFCONF, &conf);
+    if (err < 0) {
+	ucs_error("SIOCGIFCONF ioctl failed: %m");
+	status = UCS_ERR_IO_ERROR;
+	goto out;
+    }
+
+    resources     = NULL;
+    num_resources = 0;
+    for (i = 0; i < conf.ifc_len / sizeof(struct ifreq); i++) {
+	const char *name = reqs[i].ifr_name;
+
+        if (!ucs_netif_is_active(name)) {
+            continue;
+        }
+
+        tmp = ucs_realloc(resources, sizeof(*resources) * (num_resources + 1),
+                          "tcp resources");
+        if (tmp == NULL) {
+            ucs_free(resources);
+            status = UCS_ERR_NO_MEMORY;
+            goto out;
+        }
+        resources = tmp;
+
+        ucs_snprintf_zero(resources[i].tl_name, sizeof(resources[i].tl_name),
+                          "%s", UCT_TCP_NAME);
+        ucs_snprintf_zero(resources[i].dev_name, sizeof(resources[i].dev_name),
+                          "%s", name);
+        resources[i].dev_type = UCT_DEVICE_TYPE_NET;
+        ++num_resources;
+    }
+
+    *num_resources_p = num_resources;
+    *resource_p      = resources;
+    status           = UCS_OK;
+
+out:
+    if (sock >= 0) close(sock);
+    return status;
+}
+
 static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
                                                uct_tl_resource_desc_t **resource_p,
                                                unsigned *num_resources_p)
@@ -496,9 +562,9 @@ static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
 
     dir = opendir(netdev_dir);
     if (dir == NULL) {
-        ucs_error("opendir(%s) failed: %m", netdev_dir);
-        status = UCS_ERR_IO_ERROR;
-        goto out;
+	/* When /sys is unavailable, as can be the case in a container,
+	 * resort to a good old 'ioctl'.  */
+	return query_devices_ioctl(md, resource_p, num_resources_p);
     }
 
     resources     = NULL;
@@ -543,6 +609,5 @@ static ucs_status_t uct_tcp_query_tl_resources(uct_md_h md,
 
 out_closedir:
     closedir(dir);
-out:
     return status;
 }
s.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-12-09 14:13:32 +0100'>2020-12-09</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=59a6780f70e138a515dfe9c3b5b5399dbd91c228'>services: avahi: Depend on 'user-processes'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-01-19 06:09:01 +0100'>2020-01-19</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=f460f8da68f915dee5aa3ce97e05ba38c92f3106'>gnu: Use HTTPS for avahi.org everywhere.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>